TL Audio VP-1 - Manual (Page 10)

The VP-1 may be free standing, or mounted in a standard 19” rack where it will
occupy 3U of space.
4 OPERATION
4.1 Input
Select.
The VP-1 is designed to accept mic, line and instrument signals, and the relevant
source is selected via a four position selector switch. The four positions are:
Valve - selects the microphone input as the signal source, and feeds the mic signal
through an all-valve preamp circuit.
Class A - selects the microphone input as the signal source, and feeds the mic signal
through a discrete class A solid state preamp circuit.
Line - selects the line input as the source signal.
Instrument - selects the front panel instrument input as the source signal.
4.2 Input
Gain.
The Mic and Instrument gains are set simultaneously in 10dB steps by the rotary
switch, with fine adjustment available over an additional +/-15dB range from the trim
control. The total maximum gain available on the mic input is +65dB. The gain
available on the instrument input is 30dB lower than the mic, with a maximum of
+35dB.
The Line Input gain is set by the +/-15dB trim control only.
4.3
High Pass Filter (HPF).
The high pass (low cut) filter is a second order circuit (12dB per octave), with -3dB
points at the frequencies marked. The range of cut-off frequencies is fully variable
between 25Hz and 1kHz. The high pass filter is active on all inputs, and is ideal for
removing unwanted LF content from the input signal. Examples would be foot noise
and traffic rumble being picked up by a microphone, or excessive low frequency
response from a close mic’d source (known as the proximity effect). The filter is
bypassable and a status LED indicates when the filter is active.
4.4 Phase
Reverse.
The phase reverse switch is used to invert the phase of the input signal, and like the
HPF is active on all inputs. This could be required when processing a signal that is
out of phase with other signals in a mix, in which case the resultant phase error
typically appears as a loss of low frequency signal content, due to cancellation of out
of phase components. If several VP-1s are used in a multi-microphone recording
situation then some phase cancellation may occur between microphones, which the
phase reverse switch will correct.